define(function(){
	function list(){
		var $left = $(".left_a");
	    var $right = $(".left_b");
	    var $top = $(".img_3");
	$(window).scroll(function(){
		 $Top = $(document).scrollTop();
		if($Top > 800){
			$left.css("display","block");
			$right.css("display","block");
		}else if($Top <= 600){
			$left.css("display","none");
			$right.css("display","none");
		}
	})
	$(window).scroll(function(){
		$(window).scrollTop();
	})	
	$(".img_3").click(function(){
			$("html,body").animate({scrollTop:0},1000);
			
		})
	}
	return {
		list : list
	}
})
